Releasable basket

ABSTRACT

A medical retrieval device includes a basket formed of two or more loops. The basket may be used to retrieve material (e.g., a urinary stone) from a body. The basket opens and closes for end-encapsulation of a stone and is strengthened by support members that interconnect the basket loops. A captured stone may be released from the basket with the basket still in the body by opening the loops.

CROSS-REFERENCE TO RELATED APPLICATION

This is based on and claims priority to provisional U.S. patentapplication serial No. 60/060,819 which was filed on Oct. 1, 1997.

TECHNICAL FIELD

The invention generally relates to medical devices such as baskets forretrieving material from within a body. More particularly, the inventionrelates to releasable baskets for retrieval of stones such as urinarytract stones, gall stones, and other biological materials.

BACKGROUND INFORMATION

Medical retrieval baskets generally are used to retrieve biological andforeign material from the body including stones. Such baskets may beused through an endoscope or a laparoscope, for example.

In existing medical retrieval baskets, the contour of the basketsgenerally are round, oval, or pear-shaped, and the baskets are formed bya plurality of legs. Stones or other biological materials are capturedin the basket by moving the basket around the material to be retrievedand maneuvering the material into the basket through the space betweenthe basket legs.

After the material is captured in a known basket, it is generallydifficult to release the material from the basket if release of thecaptured material is required or indicated. The technical difficulty inreleasing material such as a captured stone is a characteristic of knownmedical retrieval baskets in general. In some patients withlong-standing clinical problems with urinary tract stones, a cicatrixmay form in the tract as a result of trauma to its lining. The stenosiscreated by the cicatrix may not be so narrow so as to interfere withinsertion of a retrieval basket while the basket is in a closedposition. However, after the basket is expanded to capture the stonethat is lodged beyond the stenotic area of the tract, the diameter ofthe basket containing the captured stone may exceed the diameter of thestenotic region of the urinary tract. Under these circumstances, releaseof the stone from the basket is a prerequisite for withdrawal of thedevice from the urinary tract. If the stone can not be released, moreinvasive, surgical approaches are required to disengage the stone fromthe basket.

Also, known baskets must be eased beyond the stone or to one side of thestone to permit entry of the stone into the basket. This maneuver can betechnically very difficult. The narrow diameter of the tract lumen,compounded by the formation of stretch resistant scar tissue in thetract at the situs of the stone can severely limit the space aroundwhich the basket can maneuver. Moreover, the tract lining may become soattenuated at the site of the stone that advancing the basket to oneside of the stone may risk rupture of the tract.

When expanded, existing baskets also generally lack dilatative strength.That is, known baskets generally are not resistive to forces counteringbasket expansion. The lack of dilatative strength in existing baskets isusually the result of flexible basket legs which are helpful infacilitating the entry of a stone into the basket but which decreasedilatative strength. Consequently, existing baskets generally are noteffective at dilating the tract.

SUMMARY OF THE INVENTION

The invention relates to medical retrieval baskets with enhanced basketstrength and with features that permit both end-encapsulation and, whenindicated, release of biological material. The basic medical retrievalbasket design as contemplated by the invention is an end-encapsulationbasket formed by a plurality of loops supported by members disposedbetween the loops.

Baskets according to the invention have several advantages over otherknown baskets. One advantage is the feature that allows stone capture byend-encapsulation. The basket is formed by a plurality of loops, theloops are joined at the basket base, and have an unattached end at thedistal portion of the basket. The basket loops are moveable between aclosed position and an open position. In the open position, the ends ofthe loops are parted. When the basket is maneuvered into a body tract tocapture material such as a stone, the basket is in a withdrawn positioncollapsed within the sheath. As the end of the sheath approaches thestone, the basket is extended from the sheath. The basket loops aremoved between a closed position and an open position where theunattached ends of the loops are parted. With the unattached ends of theloops parted, the basket is advanced directly over the stone at thefront end of the basket. The stone is end-encapsulated when the stoneenters the basket through the space created by the parted unattachedends of the basket loops. The end-encapsulation basket design obviatesthe need for passing the basket to one side of, or beyond, the stone inorder to capture the stone. The basket can "pluck" stones from embeddedregions such as the calyx of a kidney. Once the stone is captured in thebasket, the unattached ends of the basket loops are juxtaposed byreturning the basket loops to the closed position. The stone is therebycaptured and the medical retrieval device with the captured stone isremoved from the body tract.

Another advantage of baskets according to the invention is that theydilate the tract. Dilation of the tract around the stone permits greaterbasket maneuverability thereby facilitating stone capture. Also,dilation of the tract, as the captured stone and basket are withdrawnfrom the tract, diminishes the potential damage that may be caused tothe tract lining by ragged stone edges.

Still another advantage of a basket of the invention is the ability torelease captured material. After material (e.g., a stone) is captured inthe basket, the unattached ends of the basket loops may be parted bymoving the basket loops from the closed position to the open position.The stone then may be released from the basket between the partedunattached ends of the basket loops.

In one aspect, the invention relates to a medical device for retrievingmaterial from a body. The device comprises a proximal handle, a sheath,and a basket. The sheath extends distally from the handle and has alumen extending therethrough from a distal end of the sheath to aproximal end of the sheath. The basket is moveable relative to thesheath between a withdrawn position in which the basket is collapsedwithin the lumen of the sheath and an extended position in which thebasket extends from the distal end of the sheath and is disposed outsideof the lumen. The basket has a base and a distal portion when in theextended position, and the basket comprises at least two loops which arejoined at the base and which are unattached to each other at the distalportion of the basket. The loops are moveable when the basket is in theextended position between an open position and a closed position withthe loops being closer together at the distal portion when in the closedposition than when in the open position. This device can be used,according to another aspect of the invention, to retrieve material(biological or foreign) from a body by inserting the device, extendingthe basket from the sheath and moving the basket loops from a closedposition to an open position, capturing the biological material withinthe basket, retracting the loops into the sheath wherein the unattachedends of the loops are juxtaposed thereby moving the basket to asubstantially closed position, and withdrawing the basket from the bodyto remove the material from the body.

In one embodiment of the invention, the proximal ends of the basketloops forming the basket base are operably attached to an elongatemember (e.g., a cable or wire), and the elongate member is moveablewithin the sheath along its length. In the withdrawn basket position,the basket is collapsed within the sheath and the unattached ends of thebasket loops are together and touching. When the elongate member isadvanced, the basket is extended out of the sheath moving the basket tothe extended position and the unattached distal ends of the basket loopspart. The basket loops thereby assume an open basket loop position bythe inherent elasticity of the basket loops as movement of the elongatemember causes the loops (i.e., the basket) to extend outside of thesheath. Reversing the movement of the elongate member by withdrawing itwithin the sheath, moves the basket loops back within the sheath andcollapses them.

In another embodiment of the invention, when the basket is in theextended position, the inherent elasticity of the basket loops maintainsthe basket in the closed position, and wires are operably attached to anintermediate portion of the basket loops at one of the ends and to asecond elongate member within the sheath by the other end. Theunattached ends of the basket loops are parted when traction is appliedto the second elongate member, tensing the wires, and pulling theunattached ends of the basket loops apart. The basket loops are therebymoved from a closed position to an open position.

Other embodiments of devices according to the invention include thefollowing features. For example, a channel can be disposed through thesheath of the retrieval device, and a push rod can be axially disposedwithin the channel through the basket base and into the lumen of thebasket. The push rod can be used to push material, such as a stone, outof the basket through the parted unattached ends of the basket loops.Furthermore or alternatively, a ram-rod or other lithotriptic device canbe disposed in the channel for fragmenting the material captured andstabilized within the basket.

The basket loops can be supported by support members disposed betweenthe loops of the basket. The support members improve the basketstrength. Improved basket strength enhances stone gripping and improvesdilatative force that can be exerted by the retrieval device of theinvention.

Material such as mesh or woven material may be disposed in the loops ofthe basket. The basket loops with the disposed material within the loopsmay form opposing concave or cuplike structures for holding the capturedmaterial.

At least a portion of at least the inner surfaces of the basket loopscan be modified to improve stone gripping. For example, all or a portionof the inner surfaces of the loops can be coated with an anti-slipsubstance such as a rubberized material or roughened in some manner(e.g., by serrations, abrasions, etching, etc.) to increase frictionbetween the inner surfaces of the basket loops and the capturedmaterial.

It is possible with baskets according to the invention to remove polypssuch as gastrointestinal polyps. In such embodiments, the basket loopsare energized (e.g., with electrical energy such as RF energy) to excisea polyp. Also or alternatively, the basket loops may have a cuttingsurface. Polypectomy may be performed and the polyps preserved in thebasket for subsequent pathological examination.

The invention also contemplates methods related to the baskets such asmethods for constructing the basket loops from a single piece ofmaterial a flat, substantially oval, symmetrical template. The templatehas oppositely disposed ends and is removed from the single piece ofmaterial. As part of the manufacturing process, the material issubsequently bent and folded to form the basket structure. The bends andfolds provide elasticity to the opposed loops. The elasticity introducedby folding and bending the basket materials is taken advantage of toopen and close the basket loops.

In another aspect of the invention, a method for manufacturing a medicalretrieval basket comprises removing a flat, substantially oval templatefrom a single piece of construction material. The template issymmetrical and has a first end and a second end, with the first andsecond ends being oppositely disposed. The template is then folded suchthat the first and second ends of the template are brought together, andthe joined ends are then secured together.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also the drawings are notnecessarily to scale, emphasis generally being placed upon illustratingthe principles of the invention.

FIG. 1A is a plan view of a medical retrieval device according to theinvention with the basket in the open position.

FIG. 1B is a plan view of the medical retrieval device of FIG. 1A withthe basket in the closed position.

FIG. 1C is a plan view of a medical retrieval device with the basket inan intermediate position between closed (FIG. 1B) and open (FIG. 1A).

FIG. 1D shows a medical retrieval device according to the inventionincluding a distal basket, an intermediate sheath, and a proximalhandle.

FIG. 2A is a plan view of a medical retrieval device with the basket ina collapsed position within the sheath.

FIG. 2B is a plan view of the device of FIG. 2A with the basket in anopen position and extended outside of the sheath.

FIG. 2C is a plan view of the device with the basket in an intermediateposition between closed and open (FIG. 2B).

FIG. 3A is a plan view of basket loops according to the inventionillustrating a modification of the inner surface of the basket loops.

FIG. 3B is an expanded view of a section of a basket loop shown in FIG.3A.

FIG. 4A is a plan view of a basket of the invention in the closedposition illustrating second elongate members.

FIG. 4B is a plan view of a basket of the invention in the open positionillustrating second elongate members.

FIG. 4C is a plan view of a basket of the invention in the open positionillustrating rigid second elongate members.

FIG. 4D is a plan view of a basket of the invention in the closedposition illustrating rigid second elongate members.

FIG. 5A is a plan view of an embodiment of a basket according to theinvention including a lithotriptic device.

FIG. 5B is a plan view of an embodiment including a push rod.

FIG. 6 is a plan view of a device having a mesh disposed within thebasket loops.

FIGS. 7A-7D are diagrammatic representations of a clinical applicationof the device of FIGS. 2A, 2B, and 2C.

FIGS. 8A-8D are diagrammatic representations of another clinicalapplication of a device according to the invention wherein the basketloops excise a tissue.

FIGS. 9A-9E illustrate a method for constructing a basket according tothe invention.

DESCRIPTION

Referring to FIGS. 1A and 1D, a retrieval device according to theinvention includes basket 10, a catheter or sheath 18 for introductionof the basket 10 into a tract, and at least one cable 20 extending andmoveable within the sheath 18. As shown in FIG. 1D, the device alsoincludes a proximal handle 9 at the proximal end of the sheath 18, andthis handle typically includes one or more actuating mechanisms (e.g., aslide, a knob, a dial, etc.) coupled to the sheath 18 and/or the cable20 for causing the sheath 18 and the basket 10, under operator control,to move relative to each other to move the basket from a collapsedposition within the sheath to an extended position outside of thesheath. The cable 20 generally can be any elongate member such as acable, wire, coil, or shaft, for example. The basket 10 includes atleast two basket loops 12. Each of the basket loops 12 has an unattachedend 14 and a base or a fixed end 15.

The basket 10 is moveable between an open position and a closedposition. In FIG. 1A, the basket 10 is in an open position. When thebasket 10 is in the open position, the unattached ends 14 of the basketloops 12 are parted as shown in FIG. 1A. When the basket 10 is in theclosed position, as shown in FIG. 1B, the unattached ends 14 of theloops 12 are juxtaposed in that they are located close together. Thebasket 10 may assume any position between the open and closed positions.For example, the unattached ends 14 of the basket loops 12 may be partedto any intermediate position along an arc drawn by the unattached ends14 of the basket loops 12 as the loops move between the closed positionillustrated in FIG. 1B and the open position illustrated in FIG. 1A.FIG. 1C illustrates an exemplary intermediate position of the unattachedends 14 of the basket loops 12 between the open position of the basket10 and the closed position of basket 10.

The basket loops 12 may be any shape, for example, generally oval (asshown in FIG. 1A), round, oblong, or asymmetrical. The basket loops 12may be disposed in one or more planes as shown in FIG. 1A. Also, whiletwo loops 12 are shown and described herein, it is possible to constructa device with two or more loops 12 and such devices are within the scopeof the invention. For example, a device with three or four or more loops12 is possible.

Also, the length of each of the loops 12 (l in FIG. 1B) can be the same,or one can be slightly longer than the other such that the ends 14 donot exactly align upon closure. Having one loop longer than the otherhas been shown to help in collapsing the basket to its smallest profilesuch that it fits into a sheath 18 (FIG. 2A) easier.

Referring still to FIG. 1A, in a disclosed embodiment, the basket loops12 are strengthened by support members 16. The support members 16 arestruts disposed between the two opposing basket loops 12. The supportmembers 16 or struts help to prevent scissoring of the basket loops in ahorizontal plane and add strength to the basket in a vertical plane whenthe basket is expanded. It is possible to achieve a functioning basketwithout the members 16.

Referring to FIG. 2A, in one embodiment of the invention, the base 15 ofthe basket 10 is operably attached to a first cable or elongate member20 axially disposed within the lumen 22 of the sheath 18. The basket 10,when retained within the lumen 22 of the sheath 18, is in the collapsedposition. In one embodiment, the sheath is made of an biologicallyinert, generally flexible material. Referring to FIG. 2B, advancing thefirst cable 20 in the direction of the arrow extends the basket 10 fromthe end 24 of the sheath 18. In this embodiment, the elasticity of thebasket loops 12 causes the loops to part at their unattached ends 14thereby moving the basket from a closed position to an open position.

The basket 10 may assume any position between a closed position and anopen position depending on the extent the basket has moved beyond theend of the sheath. For example, the basket may assume the intermediateposition, illustrated in FIG. 2C. The ends 14 of the basket loops 12 mayassume any position on an arc drawn by the unattached ends 14 of thebasket loops 12 as the basket extends from fully out of the sheath tofully withdrawn within the sheath.

In the disclosed embodiment, the basket loops 10 are made from a metalmaterial. For example, basket loop material can be specialty metals suchas 455 custom stainless steel or NiTi ("Nitinol"). Alternatively thebasket loops can be made from plastic, a composite, polymer, or othermaterial. Also, the basket loops may be formed from laminations of theabove materials. In the disclosed embodiment, the basket loops are madeof flat wire (i.e., wire that is rectangular in cross section) that isabout 0.003 to 0.005 inches thick, but may be of a round, D-shape, orother cross-sectional shape.

Referring to FIG. 3A, the basket loops can have an inner surface 11 thatis designed to maximize grip on material. In one embodiment, as shown inFIG. 3B, at least a portion of the inner surface 11 is roughened byserrations or teeth. Roughening can also be achieved on the innersurfaces by etching, points, or a variety of other means. One or more ofthe basket loops may have such a rough inner surface, and it may coverall or a portion of one or more of the inner surfaces.

Referring to FIG. 4A, in an alternate embodiment, when the basket 10 isextended from the sheath 18, the basket maintains a closed position. Inthis alternate embodiment, an end of at least one wire 32 is operablyattached to an intermediate portion 34 of at least one of the basketloops 12. The wire extends into the lumen 22 of the sheath 18 and isoperably attached by its other end to a second cable or elongate member21 disposed within the lumen 22 of the sheath 18. The second cable 21may be disposed in the same or different lumens as the first cable 20.The wire 32 is kept taut by traction on the second cable 21 supplied bya mechanism at the proximal handle of the device.

With continued reference to FIG. 4A, when the second cable 21 is axiallymoved in the sheath lumen 22 in the direction indicated by the arrow,the tension on the wires 32 is increased and the ends 14 of the basketloops 12 move apart until the basket is in an open position asillustrated in FIG. 4B. The position of the basket 10 may beadditionally fine-tuned by axial movement of first cable 20. The ends 14of the basket loops 12 may assume any position along an arc drawn by theends 14 of the basket loops 12 depending on the degree of tensionimparted to the wires 32 by the traction maintained on second cable 21and first cable 20.

Referring to FIG. 4C, in another embodiment of the invention, when thebasket 10 is extended from the sheath 18, the basket 10 assumes an openposition. In this embodiment, the wires 32 are formed of stiff material.To move the basket from an open to a closed position, the first cable 21is advanced in the direction of the arrow. The stiff wires 32 push thebasket loops ends 14 closer together thereby moving the basket from anopen to a substantially closed position as shown in FIG. 4D. Furtherfine adjustment to the basket can be made by axial movement of firstcable 20.

In other embodiments of the invention, the device includes two or morebasket loops and at least one wire operably attached to at least one ofthe two or more basket loops.

Referring to FIG. 5A, in another embodiment of the invention, a channel36 is longitudinally disposed within the sheath 18 and extends throughthe fixed end 15 of the basket loops into the lumen 34 of the basket 10.A ram-rod 29 or other lithotriptic device such as, for example, a laser,is longitudinally disposed in the channel 36. In operation, a stone 31is captured in the lumen 34 of the basket 10. The ram-rod 29 is advancedin the channel beyond the fixed ends 15 of the basket loops and into thelumen 34 of the basket 10 until the end 35 of the ramrod 29 abuts thestone 31. The stone 31 is then fragmented by lithotripsy. The fragmentedstones 31 are withdrawn from the tract while encapsulated in the basket.

Referring to FIG. 5B, in an alternate embodiment of the invention, afterfragmentation of the stone, or under circumstances in which it isdesirable to release the stone from the basket, the basket 10 is movedfrom the closed position to the open position. A push rod 33 disposedwithin the channel 36 is advanced into the lumen 34 of the basket untilthe end 35 of the push rod 33 contacts the stone or stone fragment 31.The push rod 33 is advanced further into the lumen 34 of the basket 10until the stone or stone fragment 31 is pushed out of the basket lumen34 through the parted ends 14 of the basket loops 12.

Referring to FIG. 6, in yet another embodiment of the invention, thebasket loops 12 have a membrane or mesh material 40 disposed within theloops 12. The basket loops 12 serve as a frame to support the mesh ormembrane. The mesh or membrane 40 is attached to the wire loop frame byany means known to one skilled in the art. In one embodiment, asillustrated in FIG. 6, the mesh or membrane 40 of the loops 12 form aconcavity so that the lumen 34 of the basket is a pocket or iscup-shaped. The mesh or membrane 40 can be formed of polymer, membrane,wire, metal, mesh, film, cloth, fabric, textile, woven material, etc.

In operation, referring to FIG. 7A, the retrieval device is insertedinto a tract 50 of the body to retrieve biological material, forexample, a stone in the gall bladder, biliary tree, ureter, kidney, orurethra. The end of the device 24 is inserted into the tract 50 whilethe basket 10 is collapsed and enclosed within the sheath 18. Referringto FIG. 7B, the basket 10 is advanced in the body tract 50 until the endof the basket 24 approaches the stone 31. As the basket approaches thestone 31, the basket 10 is extended out of the sheath and moved from acollapsed position to an open or intermediate position. The method ofopening and closing the basket does not substantially alter theoperation of the device in capturing a stone within a tract. Referringto FIG. 7C, the basket 10 is advanced further into the body tract 50until the stone 31 is captured by end-encapsulation. End-encapsulationoccurs when the stone 31 passes between the parted unattached ends 14 ofthe open basket 10. Referring to FIG. 7D, after the stone 31 ispositioned within the lumen 34 of the basket 10, the basket 10 isreturned to a closed position. The unattached ends 14 of the basketloops 12 are substantially juxtaposed entrapping the stone 31 within thebasket 10. It is not essential to the operation of the basket that theunattached ends 14 of the basket loops 12 actually meet. Forparticularly large stones, for example, the diameter of the stone willprevent juxtaposition of the unattached ends of the basket. However, theessential feature of successful end-encapsulation for stone removal issufficient contact between the inner surface of the basket loops withthe stone surface so that the stone does not inadvertently slip out ofthe basket. The retrieval device with the entrapped stone is withdrawnfrom the body tract.

Referring to FIG. 8A, in yet another embodiment of the invention, thebasket loops may be used to excise tissue (i.e., perform a biopsyprocedure), for example a polyp 70 in the lumen of the gastrointestinaltract 72. An advantage of this embodiment of the invention is that thepolyp 70 is preserved in the basket lumen following polypectomy in acondition suitable for subsequent pathological examination. In oneembodiment, the basket loops are energized, for example, at theunattached ends 14 of the basket loops 12. In operation, as shown inFIG. 8A, the retrieval device is advanced into the lumen of thegastrointestinal tract 72, preferably under endoscopic guidance, untilthe basket 10 approaches the polyp 70. The polyp is end-encapsulatedwhen the basket 10, in the open position, is advanced over the polyp asillustrated in FIG. 8B. The polyp 70 is captured within the basket lumen34 as shown in FIG. 8C, and the basket 10 is moved to a substantiallyclosed position. Sufficient energy by any means known to one skilled inthe art is applied to the unattached ends 14 of the basket loops 12.Alternatively, the basket loops may have a cutting surface to permitexcision of the polyps. Sufficient energy is applied to the unattachedends 14 of the basket loops to separate the polyp 70 from its stalk.Referring to FIG. 8D, the polyp 70, detached from the body, drops intothe basket lumen 34. The polyp 70 within the basket lumen 34 iswithdrawn from the gastrointestinal tract 72. The polyp may be removedfrom the basket for subsequent pathological analysis.

The basket loops can be constructed according to the invention from asingle piece of material. Referring to FIG. 9A, a template 62 can becreated from the unitary piece of material, and the template can besubstantially oval and symmetrical with two oppositely disposed ends, 60and 60', two loop members 64 and 64', and support members 16. Thetemplate 62 is removed from a single piece of substantially flatmaterial by cutting, etching, stamping, extruding, or removing by anyother method known to one skilled in the art for constructing a templatefrom a single piece of material. Referring to a particularly preferredembodiment of the invention shown in FIG. 9B, following construction ofthe template 62, the ends 60, 60' of the template 62 are broughttogether to superimpose the ends on one another as indicated by thearrows in the side view of the template illustrated in FIG. 9C. The endsare then secured to one another thereby forming the three dimensionalbasket structure illustrated in FIG. 9D with the two loops. That is, themembers 64, 64' become the basket loops, as illustrated in FIG. 9D.

The inner surface 11 of basket loops 64 and 64' may be roughened, forexample, by serrations or teeth (as shown in FIG. 9E), etched surfaces,or points. One or more of the basket loops may have such a rough innersurface. The roughened surface may be incorporated in the template as itis cut, etched, extruded or stamped from a material. Alternatively, theroughened surface may be applied after the template is constructed butbefore the template is folded into a three-dimensional basket. The innersurfaces 11 of the loop members 64, 64' can instead or additionallytreated with an anti-slip material such as a plastic composite or arubberized coating before the template is folded into a threedimensional basket shape with loops.

Variations, modifications, and other implementations of what isdescribed herein will occur to those of ordinary skill in the artwithout departing from the spirit and the scope of the invention asclaimed. Accordingly, the invention is to be defined not by thepreceding description but instead by the spirit and scope of thefollowing claims.

What is claimed is:
 1. A medical device, comprising:a proximal handle; asheath extending distally from the handle and having a lumen extendingtherethrough from a distal end of the sheath to a proximal end of thesheath; and at least two opposing loops having a collapsed position inwhich the loops are collapsed within the lumen of the sheath and anotherposition in which the loops extend from the distal end of the sheath andout of the lumen, the loops being joined at a base and unattached toeach other at their distal ends, the loops being moveable between anopen position and a closed position with the loops being closer togetherat their distal ends when in the closed position than when in the openposition to allow capture and release of material, at least one of theloops having a different length from the base to its distal end than atleast one other of the loops.
 2. The device of claim 1 wherein saidsheath moves relative to the loops.
 3. The device of claim 1 furthercomprising at least one elongated member extending from the handlethrough the lumen of the sheath, and joined to the loops.
 4. The deviceof claim 1 wherein each of the loops comprise an inner surface and anouter surface.
 5. The device of claim 4 wherein at least a portion ofthe inner surface of at least one of the loops comprises a concavesurface.
 6. The device of claim 4 wherein at least a portion of theinner surface of at least one of the loops comprises a roughenedsurface.
 7. The device of claim 6 wherein the roughened inner surfacecomprises a serrated surface.
 8. The device of claim 6 wherein theroughened inner surface comprises an etched surface.
 9. The device ofclaim 6 wherein the roughened inner surface comprises a toothed surface.10. The device of claim 1 wherein the loops comprise flat wire.
 11. Thedevice of claim 1 further comprising a mesh or membrane disposed withineach of the loops.
 12. The device of claim 1 wherein the loops areformed from a single piece of material.
 13. The device of claim 1wherein the loops comprise stainless steel.
 14. The device of claim 1wherein the loops comprise a shape memory material.
 15. The device ofclaim 2 further comprising one or more support members disposed betweenthe loops to provide structural support.
 16. The device of claim 1wherein mechanisms for fragmenting or moving the material are deployedwithin the sheath lumen.
 17. The device of claim 1 wherein the loops areenergizeable to delivery energy to excise a tissue.
 18. A method forretrieving biological material from a body, comprising:inserting amedical retrieval device into a body, the device comprising a proximalhandle, a sheath extending distally from the handle and having a lumenextending therethrough from a distal end of the sheath to a proximal endof the sheath, and at least two opposing loops having a collapsedposition in which the loops are collapsed within the lumen of the sheathand another position in which the loops extend from the distal end ofthe sheath and out of the lumen, the loops being joined at a base andunattached to each other at their distal ends, the loops being moveablebetween an open position and a closed position with the loops beingcloser together at their distal ends when in the closed position thanwhen in the open position to allow capture, release, and retrieval ofmaterial, at least one of the loops having a different length from thebase to its distal end than at least one other of the loops; placing theloops in the position in which they extend from the distal end of thesheath and out of the lumen of the sheath; capturing the biologicalmaterial with the loops; and withdrawing the device from the body toremove the biological material from the body.
 19. The method of claim 18wherein the capturing step further comprises breaking the biologicalmaterial into two or more pieces within the opposing loops.
 20. Themethod of claim 18 wherein the step of capturing the biological materialcomprises capturing a calculus or a stone.
 21. The method of claim 20wherein the step of capturing the biological material comprisescapturing a kidney stone.
 22. The method of claim 20 wherein the step ofcapturing the biological material comprises capturing a ureteral stone.23. The method of claim 20 wherein the step of capturing the biologicalmaterial comprises capturing a urinary bladder stone.
 24. The method ofclaim 20 wherein the step of capturing the biological material comprisescapturing a gall bladder stone.
 25. The method of claim 20 wherein thestep of capturing the biological material comprises capturing a stonewithin the biliary tree.
 26. The method of claim 18 wherein the step ofcapturing the biological material comprises a polypectomy.
 27. Themethod of claim 18 wherein the step of capturing the biological materialcomprises a biopsy procedure.
 28. A method for manufacturing a distalend of a medical retrieval device, comprising:removing a flat,substantially oval template from a single piece of constructionmaterial, the template being symmetrical and having a first end and asecond end, the first end and the second end being oppositely disposed;folding the template such that the first and second ends of the templateare brought together to form opposing loops; and securing together thetwo ends of the template to form the distal end of the medical retrievaldevice.
 29. A method for manufacturing a distal end of a medicalretrieval device, comprising:removing a flat template from a singlepiece of construction material, the template being symmetrical andhaving two ends; folding the template such that the two ends of thetemplate are superimposed to form opposing loops; and securing togetherthe superimposed ends of the template to form the distal end of themedical retrieval device.
 30. The method of claim 29 further comprisingapplying an anti-slip material to at least one surface of the template.31. The method of claim 30 further comprising roughening at least onesurface of the template.